Figure 1 depicts the surface observations at 4:00 pm CDT, which shows a low pressure system over northwestern Ontario and a cold front moving across southern Manitoba.

According to Environment and Climate Change Canada (2018), an F0 tornado touched down at 5:30 pm CDT near Ninga, MB. The path and width of the tornado was not documented by ECCC. The tornado caused no fatalities, injuries or documented property damage.
Sources
NWS Weather Prediction Center Surface Analysis Archive. (2017). Surface analysis 21Z Sun Jun 20 2004. Retrieved from: https://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php
Environment and Climate Change Canada Data. (2018). Canadian National Tornado Database: Verified Events (1980-2009) – Public. Retrieved from: http://donnees.ec.gc.ca/data/weather/products/canadian-national-tornado-database-verified-events-1980-2009-public/